1. Field of the Invention
The present invention concerns a new terpolymer with silicon-containing side chains, a radiation-sensitive composition based on this terpolymer, as well as two processes for the lithographic treatment of a substrate by means of these compositions and corresponding processes for the production of an object, particularly an electronics component.
2. Brief Description of Relevant Art
In recent years, the extent of integration of semiconductor components has been continually increasing. The resolution capacity that can be obtained with conventional deep-UV microlithography has thus reached its limits. Normally, it is no longer possible to produce, on a substrate, conventional structures with dimensions of less than 0.25 .mu.m, as is required for the production of particularly highly integrated electronics components that have been targeted recently; these have minimal dimensions down to approximately 0.12 .mu.m. In order to be able to resolve sufficiently, in an optical manner, such fine structural elements, particularly short-wave radiation must be utilized, which generally has a wavelength between 190 and 260 nm.
Today's conventional deep-UV photoresistant materials, however, are poorly suitable for such radiation. These materials are usually based on phenolic resins as binders, for example, on novolak resins or on polyhydroxystyrene derivatives, which show a strong absorption at wavelengths below 260 nm, due to their aromatic structural elements. However, this leads to the fact that, with the use of such radiation, the side walls of the finished developed resist structures do not form the targeted right angle, but rather form a more or less oblique angle with the substrate or the resist surface, which nullifies the obtaining of optical resolution as a consequence of the use of shortwave radiation.
Photoresists without a sufficiently high proportion of aromatic components, e.g., resists based on methacrylate resins, have proven sufficiently transparent for radiation below 260 nm, but they do not have the stability in plasma etching that is customary for resists based on phenolic resins; plasma etching is a principal method for producing microstructures on silicon substrates. The plasma etching stability, as is known, is essentially based on the aromatic groups in these resists.
There have also been various solutions proposed for this problem. One solution is offered by the use of a special multilayer technique. First, an initial resin coating, commonly called a planarizing layer, is introduced onto the substrate, and this layer must not be photostructurable. A second coating, a covering layer that can be photostructured, which contains an organosilicon component instead of a component with a high content of aromatic compounds, is introduced onto this first layer. The substrate coated in this way is selectively exposed, i.e., in an image-forming way, in the conventional manner and then treated with a suitable developer, so that a desired image-forming structure is generated in the covering coating that can be photostructured. A subsequently conducted treatment in oxygen plasma leads to the fact that the organosilicon compounds contained in it are oxidized to silicon oxides, at least on the surface, and these oxides form a closed etching barrier for the oxidative decomposition of the organic material that lies underneath, particularly the planarizing layer, while the planarizing layer is removed completely in an oxidative manner on those places that are not coated by the silicon-containing covering layer.
Various compositions that can be photostructured and contain organosilicon components, which are suitable for the above-given lithographic process, are described, for example, in WO-A-94/11,788. In one type, this involves a composition based on a substance that forms acid under the effect of actinic radiation (in the following, such compounds will also be called photo acid generators) and a copolymer as binder. The copolymer comprises repeating structural units with atom groups that cleave under the catalytic effect of acid, and in this way can bestow solubility to the binder in aqueous-alkaline developers, and is also comprised of repeating structural units that contain organosilicon side chains. A typical corresponding copolyer has the following structure: ##STR1##
Compositions such as these, however, are still capable of improvement. For example, their heat form stability is still insufficient for certain requirements, because a softening might occur during treatment in oxygen plasma and as a consequence, the covering layer may soften and flow, which can lead to an imprecise formation of the etching barrier and consequently to an imprecise transfer of the desired structure onto the substrate. Further, the named polymers also very strongly absorb radiation of 193 nm wavelength, due to their content of aromatic compounds.